1. Field of the Invention
This invention relates to drain holes for discharging liquid buildup from inside pneumatic lines in gas turbine engines.
2. Summary of the Prior Art
Various types of modern machinery require the use of pneumatic lines to carry pressurized air from one location to another. Typically, this might be done for the purpose of transporting a pressurized gas such as compressed air for measuring or control purposes. As modern machinery becomes increasingly complex, machinery controls are becoming more responsive to gas and air pressures to beneficially affect machine operation.
One such current use of a pneumatic line is a compressor discharge pressure line (CDP line) on a modern gas turbine engine. This is an air signal line that functions as an input signal to an engine control for the purpose of metering fuel flow to attain a desired engine speed. Airflow of a gas turbine compressor should be a significant consideration in fuel metering control functions. The CDP air signal line provides a direct indication of the airflow of the compressor for use by the gas turbine engine control.
The CDP line itself is basically a simple tube or pipe that directly carries compressed air from the engine compressor. Because the compressed air is derived from ambient air, it will contain varying amounts of water in vaporized form. Temperature and pressure changes often cause these water vapors to condense on the inside walls of the air signal line, and if large amounts of water condense, a substantial body of free-standing water can form inside the CDP line.
In a typical gas turbine engine, free-standing water could present difficulties in engine operation. The engine often remains unused during winter months at subfreezing temperatures. The free-standing water could freeze in these conditions and block the air signal line, potentially affecting the CDP air pressure as monitored by the engine control. To prevent this scenario, air signal ines have been provided with small, round drain holes at the low point in the signal line. When the signal line carries pressurized air, the air blowing out of the drain holes effectively discharges excess water.
In order to prevent unacceptable losses of pressurized air, the drain holes are purposely made with a relatively small diameter. This, unfortunately, leads to problems when the engine is not in operation and the air in the signal lines is not pressurized. Compressed air will not blow out of the hole and, therefore, only the force of gravity will work to discharge water through the drain hole. Surface tension of the water across the drain hole can actually support significant amounts of water inside the air signal line. It has been found that with no pressure differential across it, a 0.02 inch (0.0508 cm) diameter drain hole orifice will typically retain about 0.5 inches (1.27 cm) of water above it. This might be enough to plug the signal line when the water freezes. To avoid this potential problem, a new drain hole construction is desired that will not permit surface tension to support significant amounts of free-standing water in the air signal line.
Therefore, it is an object of the present invention to provide an improved drain hole construction that will not support free-standing water inside a pneumatic line.
It is another object of the present invention to provide an improved drain hole construction that will not permit liquid surface tension at the drain hole exit to support free-standing water inside a pneumatic line when the line is not pressurized.
These and other objects of the present invention will become more readily apparent from reference to the following description taken in conjunction with the appended drawings.